Pressing devices are used for various purposes, such as, for example, pressing cable shoes onto electrical cables, but also for cutting cables or punching holes into sheet metal constructions. In order to perform these different applications on one machine, an exchangeable head system is required. To simplify matters, the different mountable heads are referred to in the following as exchangeable heads. Using the same pressing device with different exchangeable heads, it is quick and easy to change over to different applications where necessary.
However, a particular problem affecting pressing devices with exchangeable heads is the longitudinal forces being transmitted, in other words, the compressive forces produced by the pressing devices, because the coupling mechanism by which the exchangeable head is attached to the pressing device naturally has to withstand these forces and the corresponding safety requirements are relatively high. It is advantageous, therefore, to find a coupling mechanism that can be handled quickly and easily and yet offers operational safety, even with high and very high longitudinal forces.
Quick-connect coupling mechanisms are known per se. A quick-connect coupling mechanism used particularly frequently for torque transmission, especially in the field of hand machine tools, employs a solution with movable locking bodies, usually balls, which engage with corresponding grooves in the exchangeable tool in the connected state. An example of this is known from DE-2 551 125, whereby percussion drills are held in a tool holder on a machine tool in an easily exchangeable manner. Although longitudinal forces are naturally also active here, these are compressive forces (seen in relation to the machine tool/tool connection), so that there is no risk of the quick-connect coupling being released under load by the longitudinal forces and thereby representing a safety risk.
However, solutions are also known in which the same functional principle is also used with quick-connect couplings, where longitudinal forces are active, which represent traction forces in relation to the parts being connected. An example of this sort of connection is disclosed in DE-1 108 528. This specification shows a valve coupling for hose lines and pipelines. In this case, a coupling sleeve exhibits radial wall bores in which radially movable balls are disposed, which may project into a peripheral groove of a coupling plug. A spring-mounted locking sleeve prevents the balls from slipping out of the peripheral groove. Because this is an application in which pressurised fluids are conducted through connectable lines, although there is a certain safety risk, because evidently no applications involving very high fluid pressures are envisaged, additional measures do not seem necessary.
The situation is different, however, when the same functional principle is to be used in a quick-connect coupling to connect an exchangeable head to a powerful pressing device. Because relatively high pressures are used in this case (for example >50 kN), special additional measures are needed in order to guarantee safety and reliability.